1. Field of the Invention
The present invention relates to: a measurement technology and a stage technology that measure the position of a movable member, e.g., a stage, that is for moving an object; an exposure technology that uses the stage technology to expose the object; and a device fabrication technology that uses the exposure technology to fabricate a device, e.g., a semiconductor device or a liquid crystal display device.
2. Description of Related Art
Lithography for fabricating devices (electronic devices, microdevices, and the like), such as semiconductor devices and liquid crystal display devices, employs an exposure apparatus (e.g., a static exposure type—a full field exposure type—projection exposure apparatus such as a stepper, or a scanning exposure type projection exposure apparatus—scanning exposure apparatus—such as a scanning stepper) that exposes a wafer (or a glass plate and the like), which is coated with a photoresist, by projecting a circuit pattern formed in a reticle (or a photomask and the like) onto the wafer through a projection optical system. In order to reduce positional distortion and overlay error in a circuit pattern fabricated with such an exposure apparatus, laser interferometers, which use frequency stabilized lasers as light sources, are conventionally used to measure the position of the stage that positions or moves the wafer and the like.
With a laser interferometer, the refractive index of the gas in the optical path, along which the laser light propagates, fluctuates depending on, for example, the temperature, the pressure, and the humidity of the gas, and these fluctuations in turn cause fluctuations in the measurement values of the interferometer (called interferometer turbulence). Accordingly, with an exposure apparatus, it is the practice in the conventional art to reduce interferometer turbulence by using a ventilation system that ventilates temperature controlled gas to the optical path of the measurement beam of the interferometer in order to stabilize the temperature of the gas in that optical path. An exposure apparatus has recently been proposed (e.g., referred to Japanese Unexamined Patent Application Publication No. H05-2883313, and Japanese Unexamined Patent Application Publication No. H08-261718) that uses a tubular cover or the like to cover at least part of the optical path of the measurement beam in order to increase the temperature stability of the gas in the optical path of the measurement beam of the laser interferometer.
As discussed above, it is necessary to take measures against turbulence when using a laser interferometer. Nevertheless, when a stage to be measured—particularly a wafer stage of a scanning type exposure apparatus—is moved at a high speed in the vertical and transverse directions, there is a problem in that the movement of the stage causes irregular fluctuations in the gas flow, and consequently interferometer turbulence remains to a certain extent.
A purpose some aspects of the present invention is to provide a measurement technology and a stage technology that can mitigate the impact of fluctuations in the refractive index of ambient gas, an exposure technology that can improve, for example, stage positioning accuracy using the stage technology, and a device fabrication technology that uses the exposure technology.